大一计算机导论第九章.doc

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1、·Communications(242)oTheprocessofsharingdata,programs,andinformationbetweentwoormorecomputers.oConnectivity-usingcomputernetworkstolinkpeopleandresources.oTheWirelessRevolution-thewidespreaduseofmobileorwirelesstelephones.Thesinglemostdramaticchangeinconnectivityandcommu

2、nicationsinthepastfiveyearsoCommunicationssystems(243)-electronicsystemsthattransmitdatafromonelocationtoanother§Sendingandreceivingdevices-originate(send)aswellasaccept(receive)messagesintheformofdata,information,and/orinstructions§Communicationchannel–transmissionmediu

3、mthatcarriesthemessage.§Connectiondevices-convertoutgoingmessagesintopacketsthatcantravelacrossthecommunicationchannelandreversetheprocessforincomingmessages.§Datatransmissionspecifications-rulesandproceduresthatcoordinatethesendingandreceivingdevices·CommunicationsChann

4、els(244)oActuallycarrythedatafromonecomputertoanotheroPhysical(wired)-asolidmediumtoconnectsendingandreceivingdevices.§Twistedpair-hundredsofcopperwires.§Coaxialcable-ahigh-frequencytransmissioncable§Fiber-opticcable-transmitsdataaspulsesoflightthroughtinytubesofglass.oW

5、ireless(245)§Infrared-usesinfraredlightwavestocommunicateovershortdistances(line-of-sight)§Broadcastradio-usesspecialsendingandreceivingtowerscalledtransceivers,whichsendandreceiveradiosignalsfromwirelessdevices§Microwave-communicationthroughhigh-frequencyradiowavesandpr

6、ovidesline-of-sightcommunicationbutovershortdistances.Bluetoothisaformofmicrowavetransmission§Satellite-amplifiedmicrowavesthatusepoint-to-pointcommunicationtorelaydevices(satellites)orbitingtheearth.Communicationinterferencescanoccurinbadweather.·ConnectionDevices(247)o

7、Modems-connectioncomputersoveranalogphonelines.§Theconvertthecomputer’sdigitalsignaltoananalogtransmissiontosendoverthephoneline(modulation)andthenre-convertittodigitalwhenreceivinginformationfromthephonelines(demodulation).§Transferrateisinbits-per-second.§Fourtypes:Int

8、ernal,external,PCcard,andWirelessoConnectionservice(248)§Digitalsubscriberline(DSL)-usesexistingtelepho